The US accounts for about 30% of an estimated 15,000,000 dental laser procedures done per year, worldwide. Most common are laser root canal sterilization and laser sulcular debridement. Although there is overwhelming evidence that laser treatment is bactericidal, current laser systems are neither designed nor optimized for their antibacterial effects. Quantification of laser ablation of pigmented pathogens described in this application will enable the design of a novel laser system optimized for root antisepsis. Phase I: Six-month feasibility study: Develop a quantitative, predictive model. Aim 1: Determine experimentally the irradiation parameters necessary for Porphyromonas gingivalis (Pg) ablation. Aim 2: Develop a computer-based model to predict the depth of Pg destruction in root dentin. Ablation properties of Pg, measured in vitro, are incorporated into the model defined by the thermal/optical properties of Pg and dentin. The model will predict the spatial distribution of energy deposition that is lethal to Pg but benign to normal tissue. Phase II: Develop a dental laser system that incorporates an optimized irradiation format and test it clinically. A future aim is to develop laser antisepsis for other pigmented pathogens and other dental applications such as endodontic laser sterilization of root canals. Significance: The antimicrobial laser represents a potential new class of antibiotics with no known resistance, systemic side effects or negative interactions. It can access intracellular pathogens and those in certain privileged sites. The technique of laser antisepsis developed for the root surface has potential applications in other medical fields. [unreadable] [unreadable]